• Steel and Composite Structures
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• 제20권5호
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• pp.1103-1117
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• 2016

The present investigation is to study the plane problem in initially stressed thermoelastic half-space with voids due to thermal source. Lord-Shulman (Lord and Shulman 1967) theory of thermoelasticity with one relaxation time has been used to investigate the problem. A particular type of thermal source has been taken as an application of the approach. Finite element technique has been used to solve the problem. The components of displacement, stress, temperature change and volume fraction field are computed numerically. The resulting quantities are depicted graphically for different values of initial stress parameter. The relaxation time and the initial stress parameter have a significant effect on all distributions.

• Wind and Structures
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• 제19권5호
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• pp.541-563
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• 2014

This paper investigates the topographic effects on wind characteristics over hilly terrain, based on wind data recorded at a number of meteorological stations in or near complex terrain. The multiply data sources allow a more detailed investigation of the flow field than is normally possible. Vertical profiles of mean and turbulent wind components from a Sodar profiler were presented and then modeled as functions of height and wind speed. The correlations between longitudinal and vertical wind components were discussed. The phenomena of flow separation and generation of vortices were observed. The distance-dependence of the topographic effects on gust factors was revealed subsequently. Furthermore, the canyon effect was identified and discussed based on the observations of wind at a saddle point between two mountain peaks. This study aims to further understanding of the characteristics of surface wind over rugged terrain. The presented results are expected to be useful for structural design, prevention of pollutant dispersion, and validation of CFD (computational fluid dynamics) models or techniques over complex terrains.

• Structural Engineering and Mechanics
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• 제51권2호
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• pp.199-214
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• 2014

The present investigation is concerned with the effect of two temperatures on functionally graded (FG) nanobeams subjected to sinusoidal pulse heating sources. Material properties of the nanobeam are assumed to be graded in the thickness direction according to a novel exponential distribution law in terms of the volume fractions of the metal and ceramic constituents. The upper surface of the FG nanobeam is fully ceramic whereas the lower surface is fully metal. The generalized two-temperature nonlocal theory of thermoelasticity in the context of Lord and Shulman's (LS) model is used to solve this problem. The governing equations are solved in the Laplace transformation domain. The inversion of the Laplace transformation is computed numerically using a method based on Fourier series expansion technique. Some comparisons have been shown to estimate the effects of the nonlocal parameter, the temperature discrepancy and the pulse width of the sinusoidal pulse. Additional results across the thickness of the nanobeam are presented graphically.

• 한국소음진동공학회논문집
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• 제21권5호
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• pp.455-460
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• 2011

In this work, an active hybrid mount using piezostack actuator and rubber element is manufactured, and its vibration control performance is evaluated via feedforward control. A hybrid active mount featuring inertia type of piezostack actuator is proposed and manufactured. After describing the configuration of the hybrid mount, a mount system is then constructed. To attenuate vibrations from vibration sources, a feedfoward controller is experimentally implemented to the system. Vibration control performances are evaluated at each mount. Effective control performances such as accelerations are obtained and presented in frequency domains.

• 천문학회보
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• 제35권2호
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• pp.68.2-68.2
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• 2010

Diffuse interstellar atomic hydrogen (HI) gases are easily shaped into shell-like features by energetic processes such as stellar winds and supernova explosions. The physical characteristics and the Galactic distribution of HI shells and shell-like structures, therefore, are closely related to those of the energy sources. Recently, Inner-Galaxy Arecibo L-band Feed Array (I-GALFA) low-latitude HI survey has been completed. I-GALFA HI survey covers the central part of the first quadrant ($31^{\circ}{\lesssim}1{\lesssim}77^{\circ}$ at b = $0^{\circ}$, ${\mid}b{\mid}\lesssim\;12^{\circ}$) with spatial and velocity resolutions of 3.35′and 0.184 km/s, respectively. The high-angular and high-velocity resolutions enable in-depth investigation of HI shells including the ones of smaller angular sizes. We have found 36 shell candidates with the naked eye. Their angular sizes are distributed from $\sim0.4^{\circ}$ to $\sim12^{\circ}$. About sixteen of them appear to be expanding. We examine associated features at other wavebands and discuss their origin.

• 한국환경보건학회지
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• 제20권1호
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• pp.19-27
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• 1994

This paper reports an investigation of concentrations major carcinogenic indoor air pollutants for radon, formaldehyde, and asbestos in the 83 subway stations in the Seoul metropolitan area during November 1991~September 1992. Mean concentrations of indoor pollutants in Seoul subway stations surveyed were 0.23 ppb for formaldehyde, 1.12 pCi/l for radon, and 0.008 fiber/cc for asbestos. Mean formaldehyde concentrations in 83 subway stations were below the U.S. EPA formaldehyde standard (100 ppb), whereas mean concentrations of radon and asbestos in 2% and 22% of total sampled subway stations exceeded the U.S. radon (4 pCi/l) and asbestos (0.01 fiber/cc) standand, respectively. It is likely that possible sources for radon and asbestos are radon intrusion from the leaking underground water and construction materials, respectively.

• 한국환경과학회:학술대회논문집
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• 한국환경과학회 2003년도 International Symposium on Clean Environment
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• pp.113-118
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• 2003

An investigation has been carried out on collision-induced dissociation (CID) in the development of an analytical protocol for the determination of polycyclic aromatic hydrocarbons (PARs) by ion trap tandem mass spectrometry. Two different considerations were used to choose the optimal CID conditions for complex matrix environmental samples, namely, to determine the highest signal-to-noise (SIN) ratio and the other to eliminate the background interferences originated from complex matrix samples. The PAR content of agricultural soil was measured to estimate overall distribution of PAR in throughout the country, we collected and analyzed 226 soil samples from paddy and upland soil. The average content of total PAR in all samples was 236 ${\mu}g$ $kg^{-1}$, and the range was from 23.3 to 2, 834 ${\mu}g$ $kg^{-1}$. The overall distribution of PAR was found to be closely related to the pollution sources, the size of city and the type of industry.

• Structural Engineering and Mechanics
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• 제30권5호
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• pp.577-592
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• 2008

Laplace-Fourier transform techniques are used to investigate the interaction caused by mechanical, thermal and microstress sources in a generalized thermomicrostretch elastic medium with temperature-dependent mechanical properties. The modulus of elasticity is taken as a linear function of reference temperature. The integral transforms are inverted using a numerical technique to obtain the normal stress, tangential stress, tangential couple stress, microstress and temperature distribution. Effect of temperature dependent modulus of elasticity and thermal relaxation times have been depicted graphically on the resulting quantities. Comparisons are made with the results predicted by the theories of generalized thermoelasticity. Some particular cases are also deduced from the present investigation.

• 대한기계학회논문집A
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• 제29권6호
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• pp.828-834
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• 2005

Recently, injection molded plastic optical products are widely used in many fields, because injection molding process has advantages of low cost and high productivity. However, there remains residual birefringence and residual stresses originated from flow history and differential cooling. The present study focused on developing a technique to measure the birefringence in optical plastic parts using R-G-B separation of white light. The main idea of an analysis comes from the fact that more information can be obtained from the distribution of retardation caused by different wavelengths. A complete system to give the quantitative values of retardation covering high order 2-D birefringence will be demonstrated. Further investigation is under way to improve the accuracy of the system using diodes as light sources.

• ALGAE
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• 제31권3호
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• pp.189-204
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• 2016

Microalgal bioremediation of CO₂, nutrients, endocrine disruptors, hydrocarbons, pesticides, and cyanide compounds have evaluated comprehensively. Microalgal mitigation of nutrients originated from municipal wastewaters, surface waters, and livestock wastewaters has shown great applicability. Algal utilization on secondary and tertiary treatment processes might provide unique and elegant solution on the removing of substances originated from various sources. Microalgae have displayed 3 growth regimes (autotrophic, heterotrophic, and mixotrophic) through which different organic and inorganic substances are being utilized for growth and production of different metabolites. There are still some technology challenges requiring innovative solutions. Strain selection investigation should be directed towards identification of algal that are extremophiles. Understanding and manipulation of metabolic pathways of algae will possible unfold solution to utilization of algae for mitigation of dissolve organic nitrogen in wastewaters.